Downflow centrifugal separator units of the type having an outer tube and a concentric inner tube defining an annular passageway therebetween and with slots in the lower portion of the inner tube and a separator vessel containing such units are described in detail and claimed in my prior copending application Ser. No. 092,343, filed Nov. 8, 1979, now U.S. Pat. No. 4,279,624, which is a continuation of application Ser. No. 947,173, filed Sept. 28, 1978.
The present invention relates to a multi-station downflow centrifugal separation method and apparatus in which improved downflow centrifugal separator units of the type described and claimed in said copending patent application are employed in a sequence of units of decreasing diameters positioned in a sequence of stations or levels (tiers) in a large separator vessel and wherein the particulate-laden gas enters the top of the large vessel and purified gas exits from the bottom of this vessel with bleed gas plus collected particles being continuously removed from each of these levels.
Separator vessels embodying the present invention are particularly useful for separating particles of catalyst from hydrocarbon vapors issuing from a catalytic cracking process and can also be advantageously utilized in other applications such as for removing suspended solids from the gaseous products of combustion coming from pressurized fluidized bed combustion of pulverized solid fuel for cleaning these gases before they are fed into a gas turbine. The multi-station downflow centrifugal separation method and apparatus of this invention are useful for separating particles from the gases resulting from coal gasification and liquefaction, and for use with supercharged boilers.
Highly efficient separation of particles as provided by the present invention is quite important for air pollution control purposes and power generation purposes. Active large catalyst particles can advantageously be recovered and reused by this separation. Furthermore, purified clean gas from a multi-station (multi-tier) downflow centrifugal separator vessel embodying this invention can be used to drive a turbine for generating valuable power and without any significant erosion of the turbine blades, which would otherwise be caused if many particles of unduly large size were present in the gas stream being fed into the turbine. It turns out in actual practice that the blades of a turbine will experience excessive erosion if there are any significant numbers of particles ten microns in size or larger in the gas stream entering the turbine. A multi-station downflow separator vessel embodying this invention will effectively remove particles down to a size of six microns and even smaller from a gas stream.
The prior art separator vessels containing multiple tubular type units, for example as shown in U.S. Pat. No. 2,941,621, are not very effective in maintaining high fractional separation efficiencies due to "coupling" effects between the respective tubular separator units operating in parallel in the vessel as a whole. Such "coupling" effects cause the particle discharge from one tubular unit in the vessel to flow in a reverse direction into what would normally be the particle discharge of a second tubular unit neighboring the first. Thereby separated particles of various sizes which are separated by the first unit find their way into what would normally be the clean gas outlet of the second unit, and contaminate the output of the whole prior art vessel. Consequently, in the output of the prior art separator vessel, there are significant numbers of larger particles. The separation and removal of all particles larger than the intended maximum permitted particle size has not in fact occurred, even though the tubular units in the vessel when individually tested will remove all particles larger than said permitted size.
This failure in actual practice to remove all particles larger than a given permitted maximum size is called a failure to maintain high fractional separation efficiencies. The results of this failure in the prior art to maintain high fractional separation efficiencies are far more deleterious than appear at first glance, because the abrasion and erosion caused by relatively few larger particles are many, many times greater than those caused by numerous smaller particles of a size below the maximum desired limit.
The fractional separation efficiencies provided and maintained by the separator vessel described in detail and claimed in said prior copending application (now U.S. Pat. No. 4,279,624) identified above are high, and the fractional separation efficiencies provided and maintained by the multi-station downflow centrifugal separator vessel described herein may be even higher, when careful design of all stations is practiced.
As explained above, multi-station downflow separator vessels of this invention can be used to advantage for separating particles from gases in a wide variety of applications in addition to purifying a gas stream for entry into a turbine.